The invention relates to an image display device comprising a light modulation panel, an illumination device facing the light modulation panel and a light source coupled to the illumination device, said illumination device comprising at least one separating layer which has at least one flat surface extending parallel to the light modulation panel and a serrated surface situated on a side remote from the flat surface, said serrated surface having a plurality of sawtooth-shaped, juxtaposed projections which are each bounded by a first and a second separating surface.
An image display device of this type is used in, for example, head-mounted displays (HMDs) and projection televisions. LCDs which are either transmissive or reflective are regularly used as light modulation panels. In a reflective LCD, the LCD is illuminated from the same side as the side from which it is viewed. In transmissive LCDs, the LCD is illuminated from a different side than that from which it is viewed. Notably for HMDs, the light source and the associated illumination device should be as thin as possible so that the HMD can be given a relatively compact form. Reflective LCDs are preferably used in HMDs. If the illumination device is relatively thin, it has the additional advantage that a lens situated on a side of the illumination device remote from the light modulation panel can be arranged relatively close to the illumination device, which is favorable for achieving an optimal magnification.
In such an image display device known from European patent application EP-A1-0 948 755, the illumination device comprises two layers connected to each other by means of a serrated surface. One layer has a single refractive index and the other layer has two refractive indices, one of which corresponds to the refractive index of the first layer. The first and second separating surfaces of the serrated projections both enclose acute interior angles with the flat surface of the separating layer.
In this patent application, an interior angle is understood to be an angle between a separating surface and the flat surface of the separating layer, measured by the material of the separating layer. An obtuse angle is herein understood to mean any angle which is larger than 90xc2x0, whereas an acute angle is understood to mean any angle which is smaller than 90xc2x0.
The unpolarized light coming from the light source is coupled into both layers, while one refractive index applies to one direction of polarization and the other refractive index applies to the other direction of polarization. In combination with the choice of both acute interior angles, the known illumination device ensures that only light having a desired direction of polarization is deflected to the light modulation panel. The light modulated by the light modulation panel is subsequently passed through the illumination device. Then, the modulated light beam is refracted.
It is an object of the invention to provide an image display device comprising a relatively compact illumination device.
In the image display device according to the invention, this object is achieved in that the first separating surface encloses an acute interior angle with the flat surface, whereas the second separating surface encloses an obtuse interior angle with the flat surface. Since the second separating surface encloses an obtuse interior angle with the flat surface, each projection will extend partly beyond a juxtaposed projection.
A light beam from the light source is reflected on the second separating surface in the direction of the light modulation panel. By choosing the obtuse interior angle, substantially any desired deflection of the light beam can be realized. In transmissive light modulation panels, the light beam is subsequently passed further on a side remote from the separating layer.
For use in reflective light modulation panels, use is to be made of a separating layer having a first and a second refractive index, in which the first refractive index applies at least to the separating layer for the light beam coming from the light source and the second refractive index applies to the light beam modulated by the light modulation panel. A light beam from the light source is reflected on the second separating surface with the first refractive index in the direction of the light modulation panel. Subsequently, the light beam is modulated by the light modulation panel and its direction of polarization is reversed. The light beam is subsequently again reflected in the direction of the separating layer, with the second refractive index applying to the light beam modulated by the light modulation panel. By choosing the obtuse interior angle and the two refractive indices, substantially any desired deflection of the light beam can be realized.
If the illumination device is provided between the separating layer and the light modulation panel with an optical element also having the second refractive index, the light beam modulated by the light modulation panel will no longer be deflected on the separating surfaces.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.